A great variety of drip irrigation apparatus is known in the marketplace and is described in the patent literature. An early disclosure of a vortex-type drip irrigation emitter is found in Israel Pat. No. 30618 of the present applicant. The first continous drip irrigation hose is described in Israel Pat. No. 45211. A further development of continous drip irrigation hoses appears in applicant's UK Pat. No. 2,069,803 which described hoses wherein emitter inserts of variable spacing and capacity are incorporated in a continuous hose preferably in accordance with computer control based on the contours of the land at which they are to be installed.
A pressure controlled continuous emitter hose is described in applicant's South African Pat. No. 82/5043.
Various types of emitter labyrinth configurations are described in the patent literature. Subsequent to applicant's Israel Pat. No. 30618, there appear Israel Pat. No. 34566 which illustrates a back and forth flow path, Israel Pat. No. 36901 which specifies certain details of the tooth and flow path configurations defined by the labyrinth, and Israel Pat. No. 45465 which specifies the relationship between tooth tip width and the flow path dimensions and the coaxial, non-overlapping relationship of the tips of the opposite facing adjacent teeth in the labyrinth. The last three prior art patents all relate to non-vortex type drippers.
Additionally, there exists a large body of literature relating to the design, construction and operation of drip irrigation emitter flow path labyrinths in engineering literature relating to hydrodynamics which is used, for example, in the design of fluid seals.
There exists a fundamental problem and limitation in all known drip irrigation systems, the collection of sediment in the emitter labyrinth passages, resulting in partial or even complete blockage thereof. This problem is dealt with in conventional drip irrigation systems of which the last three patents described above are examples, by periodic backflushing.